The objective of this research is to study the performance of surgical masks which have historically been used only as barriers to prevent exhaled particles from infecting a patient in surgery, but are increasingly used today in medical and dental care environments to protect the healthcare worker from airborne and aerosolized bloodborne pathogens. The aerosol penetration will be measured from 0.1 to about 5 mum in particle size for flowrates up to 100 L/min. An aerodynamic particle sizer will measure the supermicrometer-sized aerosols and a laser aerosol spectrometer, calibrated for aerodynamic size, will measure the submicrometer-sized aerosols. Aerosol penetration and pressure drop data will be related to each other and will be analyzed with respect to filter material and mask type (flat vs. molded cone). Models will be developed that consider all the filtration mechanisms and will be compared to the experimental data. Performances will be evaluated on masks that have been wetted, as may occur from liquid splashing or liquid adsorption during exhalation of warm, humid air. Edge leakage will be measured relative to filter penetration. Circular leak channels will be differentiated from rectangular ones and will be related to each other. The Bacterial Filtration Efficiency test will be analyzed as to the particle size distribution of its spray. The size distribution (which is the primary parameter affecting aerosol penetration) will be measured for several liquids, with and without different bacteria. The sprays will be size measured upon generation and after mixing with dry air when only the residues are left. The size-dependent penetration of inert and biologically active test aerosols will be compared with each other. New bacterial testing methods will be studied which can detect bacteria directly.